Sewing principle of sewing machine

Just like cars, the basic principles of most sewing machines are the same. The core of a car is the internal combustion engine, and the core of a sewing machine is the coil stitching system.

The loop stitching method is very different from ordinary hand sewing. In the simplest form of hand stitching, the sewist ties a piece of thread through a small eye at the end of a needle, then threads the needle and thread completely through two pieces of fabric, from one side to the other, and then back to the original side. This way, the needle drives the thread in and out of the fabric, sewing them together.

Instead, the sewing machine only pushes the needle partially through the fabric. On a machine needle, the eye of the needle is just behind the tip, not at the end of the needle.

The needle is fixed to a needle bar, which is pulled up and down by a motor through a series of gears and cams (more on this later).

As the tip of the needle passes through the fabric, it pulls a small loop from one side to the other. A device underneath the fabric grabs this loop and wraps it around another thread or another loop of the same thread. In the next two sections, we will see how exactly this system works.

The simplest coil stitch is the chain stitch. To create a chain stitch, your sewing machine will loop the same length of thread behind the thread. The fabric sits on a metal plate beneath the needle and is held in place with a presser foot. At the beginning of each stitch, the needle pulls a loop through the fabric. A loop-making device catches the loop before the needle is pulled out, and the device moves in synchrony with the needle. Once the needle pulls out the fabric, the feed dog mechanism (described later) pulls the fabric forward.

When the needle passes through the fabric again, the new loop will pass directly through the middle of the previous loop. The coil making device will grab the thread again and make the coil around the next coil. This way, each coil holds the next coil in place.

The main advantage of chain stitching is that it can be stitched very quickly. However, it is not particularly strong and if one end of the thread comes loose, the entire stitch may come loose. Most sewing machines use a stronger stitch called a whipstitch. You can see how a typical overlock stitching device works in the animation below.

The most important elements of a lockstitch device are the shuttle hook and spool assembly. A spool is simply a roll of thread placed underneath the fabric. It is located in the center of the shuttle, which is rotated by a motor in synchronization with the movement of the needle.

As with the chain stitch, the needle pulls one loop through the fabric, rises again as the feed dog moves the fabric forward, and slips another loop through. However, instead of joining different coils together, this stitching mechanism joins them with another length of thread that has been unwound from the spool.

As the needle slips the thread into the loop, the rotating shuttle catches the loop with the crochet hook. As the shuttle rotates, it pulls coils around the thread coming from the spool. This makes the stitching very strong.

This kind of rotary shuttle also evolved from the straight shuttle.

The loop stitching principle of sewing machines has evolved from straight shuttle to rotary shuttle, and has entered a mature stage.